The ISO standard family 11898-1 through -5, for example, describes a Controller Area Network (CAN) as well as an extension of the CAN called “time-triggered CAN” (TTCAN), referred to in the following also as standard CAN. The media access control method used in the CAN is based on a bit-wise arbitration. In bit-wise arbitration, multiple subscriber stations are simultaneously able to transmit data via the channel of the bus system, without thereby interfering with the data transmission. Furthermore, the subscriber stations are able to ascertain the logical state (0 or 1) of the channel while transmitting a bit over the channel. If a value of the transmitted bit does not correspond to the ascertained logical state of the channel, the subscriber station terminates the access to the channel. In CAN, the bit-wise arbitration is usually carried out on the basis of an identifier within a message that is to be transmitted via the channel. After a subscriber station has sent the identifier to the channel in its entirety, it knows that it has exclusive access to the channel. The end of the transmission of the identifier thus corresponds to a beginning of an enable interval, within which the subscriber station is able to use the channel exclusively. According to the CAN protocol specification, other subscriber stations may not access the channel, that is, send data to the channel, until the sending subscriber station has transmitted a checksum field (CRC field) of the message. Thus, an end point of the transmission of the CRC field corresponds to an end of the enable interval.
The bit-wise arbitration thus achieves a non-destructive transmission, via the channel, of those messages that won the arbitration process. The CAN protocols are particularly suited for transmitting short messages under real-time conditions, a suitable assignment of the identifiers being able to ensure that particularly important messages will almost always win the arbitration and be sent successfully.
With the increasing networking of modern vehicles and the introduction of additional systems for improving driving safety for example or driving comfort, the demands grow on the quantities of data to be transmitted and the latency periods admissible in the transmission. Examples are driving dynamics control systems such as, e.g., the electronic stability program ESP, driver assistance systems such as, e.g., the automatic distance control ACC, or driver information systems such as, e.g., the traffic sign detection (cf. for example descriptions in “Bosch Kraftfahrtechnisches Handbuch,” 27th edition, 2011, Vieweg+Teubner).
DE 103 11 395 A1 describes a system in which asynchronous, serial communication is able to take place alternatively via an asymmetrical physical protocol or via the symmetrical physical CAN protocol, and thereby a higher data transmission rate or data transmission reliability is achievable for the asynchronous communication.
DE 10 2007 051 657 A1 provides for the use of an asynchronous, fast, non CAN-compliant data transmission in the exclusive time windows of the TTCAN protocol in order to increase the transmitted data quantity.
G. Cena and A. Valenzano, in “Overclocking of controller area networks” (Electronics
Letters, vol. 35, No. 22 (1999), p. 1924) deal with the effects of overclocking the bus frequency in subsections of the messages on the effectively achieved data rate. The adaptation of data transmission reliability is not discussed.
It is clear that the related art does not provide results that are satisfactory in every respect.